Abnormal shape of the cavum septi pellucidi: an indirect sign of partial agenesis of the corpus callosum.

OBJECTIVE

To describe and assess the presence of a new indirect sign of partial agenesis of the corpus callosum (pACC): an abnormally shaped cavum septi pellucidi (CSP).

METHODS

We analyzed retrospectively images from all 71 cases of pACC seen at two referral centers between September 2006 and April 2014. Abnormally shaped CSP was diagnosed when its lateral dimension was greater than its anteroposterior dimension in the axial transthalamic plane, and the incidence of this sign was assessed. We also examined the following variables: gestational age at referral, indication for referral, which (if any) of the four corpus callosal segments were abnormal, presence of other, previously established, indirect signs of callosal agenesis (ACC) and presence of additional cerebral or extracerebral anomalies.

RESULTS

In 56 of the 71 (79%) cases, the CSP was measurable; it was abnormally shaped in 19 (34%) of these cases, 15 (79%) of which had no other indirect signs of pACC. Of 23 cases with isolated pACC and no other indirect signs, 12 (52%) had an abnormally shaped CSP.

CONCLUSIONS

In a significant proportion of cases of pACC detected prenatally, the shape of the CSP is abnormal. This should be considered an additional indirect sign of pACC, and is frequently the only clue to the diagnosis. When observing this sign in a screening context, pACC should be considered, and an attempt to visualize the corpus callosum directly in the midsagittal plane is suggested.